Inductive energizing circuit for arc plasma generator

ABSTRACT

The present invention generally relates to a method and apparatus for controlling the running, as well as the starting and shut-down operations, of a shutdown arc plasma generator or the like whose spaced-apart electrodes are energized from a circuit including an inductor which is connected in series with the electrodes and their energizing voltage source and which functions to damp out current pulsations, particularly those occurring at high mass flow rates within the arc plasma generator. Moreover, by maintaining the electrode arc discharge current constant, the arc rotation rate is also more uniform. Due to the fact that the series inductor causes current buildup in the electrode energizing circuit to be a function of time, suitable means are provided for delaying the establishment of the electrode arc discharge until such time as the circuit current has been built up sufficiently to insure that the arc discharge will be sustained. Moreover, means are also provided for decoupling the inductor from the remainder of the electrode energizing circuit, prior to the time when the electrode energizing circuit is open-circuited, so as to prevent arcing at the switch or circuit breaker means utilized to open the electrode energizing circuit.

United States Patent FOREIGN PATENTS 627,193 8/1949 Great Britain Primary ExaminerRaymond F. Hossfeld Attorneys-.1 ustin P. Dunlavey and John O. Tresansky ABSTRACT: The present invention generally relates to a method and apparatus for controlling the running, as well as the starting and shut-down operations, of a shutdown arc plasma generator or the like whose spaced-apart electrodes are energized from a circuit including an inductor which is connected in series with the electrodes and their energizing voltage source and which functions to damp out current pulsations, particularly those occurring at high mass flow rates within the arc plasma generator. Moreover, by maintaining the electrode arc discharge current constant, the arc rotation rate is also more uniform. Due to the fact that the series inductor causes current buildup in the electrode energizing circuit to be a function of time, suitable means are provided for delaying the establishment of the electrode arc discharge until such time as the circuit current has been built up sufiiciently to insure that the arc discharge will be sustained. Moreover, means are also provided for decoupling the inductor from the remainder of the electrode energizing circuit, prior to the time when the electrode energizing circuit is open-circuited, so as to prevent arcing at the switch or circuit breaker means utilized to open the electrode energizing circuit.

[72] Inventors Richard T. Cusick Laurel; Edgar A. Bunt, Kensington, Md. [21 Appl. No. 678,973 [22] Filed Oct. 30, 1967 [45] Patented May 4, 1971 [73] Assignee the United States of America as represented by the Secretary of the Navy [54] INDUCTIVE ENERGIZING CIRCUIT FOR ARC PLASMA GENERATOR 6 Claims, 2 Drawing Figs.

[52] U.S.Cl 315/111, 313/231, 313/161 [51] Int. Cl H0lj 7/24 [50] Field oiSearch 313/231; 315/102, 100 (U), 111, 125, 126, 243, 313, 322, 323, 362

[56] References Cited UNlTED STATES PATENTS 1,154,320 9/1915 Kenyon 315/126 1,582,671 4/1926 Eschholz 315/1 25X 2,373,402 4/1945 Lec0rquillier.... 315/243 2,103,030 12/1937 Dorgelo 315/100X 3,178,610 4/1965 Moerkens et a1. 315/244 3.274.424 9/1966 Bunt et a1. 313/231 INDUCTIVE ENERGIZING CIRCUIT FOR ARC PLASMA GENERATOR BACKGROUND OF THE INVENTION The heat producing capabilities of such an arc plasma generator are, of course, dependent upon the operating pressures, arc discharge current value, etc., of the generator. It is therefore desirable to operate an arc plasma generator at constant discharge current and maximum pressure. More specifically, the present invention is particularly adapted for use with a plasma arc generator comprising an arc chamber containing a pair of spaced-apart, annular or ringlike electrodes between which the arc discharge is established and around which the arc rotates at a rate dependent upon arc discharge current magnitude, during generator operation. Oneform of arc plasma generator with which the present invention has application is described in the US. Pat. issued to E. A. Bunt et al., No. 3,274,424, dated Sept. 20, 1966.

DESCRIPTION OF THE INVENTION It is proposed in accordance with the present invention to incorporate a series connected inductor in the energizing circuit to the electrodes of a DC are plasma generator for the purpose of maintaining the arc discharge current and therefore also the arc rotation rate substantially constant. As a result, the arc generator is capable of operating at higher voltages, pressures and mass flow rates than were possible in the arc plasma generators heretofore proposed. Moreover, inasmuch as the inductor is utilized in the electrode energizing circuit, it is also proposed to include means to facilitate arc generator starting, by delaying the establishment of the electrode arc discharge until the energizing current has built up to a value sufficient to insure that the arc discharge, once established, will be sustained and also means to facilitate shutdown procedure, by decoupling the inductor from the remainder of the energizing circuit whenthe main circuit breaker or switch is opened to deenergize the arc plasma generator.

In view of the foregoing, one object of the present invention is to provide a method and apparatus for controlling the running, as well as the starting and shutdown of a DC are plasma generator or the like having an inductive electrode energizing circuit.

Another object of the present invention is to provide an improved energizing circuit for the electrodes of an arc plasma generator or the like, including an inductor which functions to maintain the arc discharge current and therefore arc rotation rate substantially constant, and to provide a methodand apparatus for controlling the starting and shutdown of the plasma generator or the like.

Other objects, purposes and characteristic features of the present invention will in part be pointed out as the description of the invention progresses and in part be-obvious from the accompanying drawings, wherein:

FIG. 1 is a circuit diagram of one embodiment of the electrode energizing circuitry proposed in accordance with the present invention; and

FIG. 2 is a plot of energizing current and electrode voltage versus time when employing the energizing circuitry of FIG. 1.

Referring now to FIG. 1 of the drawings, the improved cner gizing circuitry of the present invention is particularly adapted for use with an arc plasma generator of the type described in the above-mentioned E. A. Bunt et al. patent and having a pair sistors 16 and 17 which are intended here to represent, respectively, the internal resistance of the battery 14, for example,

and the resistance of the inductive member 15. A suitable switch 18 is connected, for reasons to be described in more detail hereinafter, across the inductor 15 in circuit multiple.

A fused horn gap 19 is connected across the electrodes 11 and 12, for purposes also to be described hereinafter, and includes 'a fuse wire 20 of predetermined size selected so that current is momentarily routed away from the electrodes 11 and 12, after the switch 13 is closed to complete the energizing circuit to the electrodes. More specifically, the fused horn gap 19 functions, in-combination withthe starting wire 21, to delay the establishment of an arc discharge current between the electrodes 11 and 12, until such time as the current in the electrode energizing circuit has built up to a value sufficient to sustain an arc discharge at the electrodes, as will be described hereinafter.

The starting wire 21 is connected across the electrodes 11 and 12 and is formed with a small gap or discontinuity 22, for example, of about 0.01 inch. As a result, the starting wire will not initiate or strike the are between electrodes 11 and 12 until the fused horn gap 19 operates'or blows out. After the arc is struck, the cold input gas stream is transformed into a high temperature plasma, which is then discharged from the pressure chamber 10 through a suitable orifice (not shown).

To enable an operator to monitor the electrical connection of the bridge wire 21 with the electrodes 11 and 12, a resistor 23 is connected across the gap or discontinuity 22. This resistor 23 might, for example, have a value of 500K ohms and permits connection of a suitable meter which forms a continuity check for the bridge wire segments and electrodes, before the arc plasma generator is fired.

As an alternative to using the thin starting wire 21, having the gap or discontinuity 22, and the horn gap 19, the desired delay in the striking of the arc can be achieved by employing a single piece of thicker wire connected across the electrodes.

In order to understand the operation of the illustrated energizing circuitry of the present invention, assume first that the switch or circuit breaker 13 is operated to its closed position, with switch 18 initially open; thereby connecting the battery 14 across the electrodes 11 and 12. As mentioned previously, the fused horn gap 19 causes the initial current buildup in the circuit (see curve portion 24 in FIG. 2) to occur through the fused horn gap 19 rather than across the electrodes 11 and 12; i.e., the size of the horn gap fuse wire 20 is preselected so that the horn gap 19 shunts the electrodes 11 and 12 during that time that it takes for the current in the energizing circuit to build up to such a value that the voltage then available to be used across the electrodes 11 and 12 is sufficient to sustain any arc established therebetween. This necessary time delay in the establishment of the main arc across electrodes 11 and 12 is designated, on current curve A in FIG. 2, by the time t When the fuse wire 20 disintegrates and horn gap 19 then blows out, for example at time t, in FIG. 2, the voltage then available across the electrodes 11 and 12 easily breaks down the small gap or discontinuity 22 in the starting bridge wire 21 and so ignites the main are between the electrodes 11 and 12.

Inasmuch as the inductor 15 is now connected in series between the electrodes 11 and 12 and their voltage power source 14, the well-known properties of the inductor 15 maintain the electrode arc discharge current substantially constant by preventingcurrent pulsations. This, in turn, enables the arc plasma generator to be operated at very high mass flow rates.

When the illustrated energizing circuitry is utilized with an arc plasma generator of the type described in the above-mentioned E. A. Bunt et al. patent, the maintaining of the arc 'discharge current substantially constant also results in a more uniform rotation of the are about the electrodes. A better understanding of how the inductor 15 functions to maintain arc current constant can be had by referring to FIG. 2 and noting the manner in which electrode voltage (see curve B) is automatically varied by the inductor l5 whenever the arc current (see curve A) attempts to vary.

The shorting switch 18 of FIG. 1 functions to dissipate the stored energy of the inductor when it is time to shut down the arc plasma generator. More specifically, the shorting switch 18 is normally in its open position, as illustrated, while the arc generator is operating, and is adapted to be closed just before the main circuit breaker or switch 13 is opened to energize the electrodes 11 and 12. In other words, just before switch 13 is opened, the switch 18' is closed to dissipate the stored energy of the inductor 15 and thereby prevent arcing at the switch 13. v

Many modifications, adaptions and alterations of the present invention are possible in the light of the above teachings. It is therefore to be understood at this time that within thescope of the appended claims, the invention may be practiced otherwise than as specifically described.

We claim:

1. A method for controlling the starting and shut-down of a DC are plasma generator or the like having a pair of spacedapart electrodes which are energized by a circuit including a .DC voltage source and a series-connected inductor, compris- 2. The method specified in claim 1 wherein the step of delaying the initiation of said electrode are discharge is accomplished by shunting the electrodes for a predetermined time interval.

3. In combination with a DC are plasma generator having a pair of spaced-apart electrodes,

a DC voltagesource operably connected across said electrodes for establishing an arc discharge current between said electrodes,

an inductor connected in a series circuit with said voltage source and said electrodes for maintaining said arc discharge current at a substantially constant magnitude,

a first switch means connected in circuit series with said voltage source, said inductor and said electrodes for opening and closing said series circuit,

second switch means connected in circuit multiple with said inductor for shorting out said inductor prior to opening of said series circuit by said first switch means, and

means connected in circuit parallel with said spaced-apart electrodes for delaying the establishment of an arc discharge between said electrodes until the voltage available across said electrodes is sufficient to maintain said are discharge.

4. The combination specified in claim 3 wherein said are delaying means comprises,

' a fused horn gap means connected in circuit parallel with said electrodes and including a fusing wire selected to delay the establishment of an arc discharge between said electrodes until the voltage available across said electrodes is sufficient to maintain said are discharge.

5. The combination specified in claim 4 further including a starting wire means connected across said electrodes to facilitate the establishment of said are dischar e.

6. The combination specified in claim 5 w ereln said starting wire means is provided with a discontinuity adapted to relay the establishment of said are discharge and further including,

a monitoring resistor connected across the discontinuity in said starting wire to permit detection that the ends of said starting wire are in electrical contact with said electrodes. 

1. A method for controlling the starting and shut-down of a DC arc plasma generator or the like having a pair of spaced-apart elecTrodes which are energized by a circuit including a DC voltage source and a series-connected inductor, comprising the steps of, closing said electrode energizing circuit, delaying the initiation of an arc discharge between said electrodes until the voltage available across said electrodes is sufficient to sustain said arc discharge, short circuiting said inductor to dissipate the stored energy thereof when it is desired to shut down said arc plasma generator or the like, and subsequently opening said electrode energizing circuit to deenergize said electrodes.
 2. The method specified in claim 1 wherein the step of delaying the initiation of said electrode arc discharge is accomplished by shunting the electrodes for a predetermined time interval.
 3. In combination with a DC arc plasma generator having a pair of spaced-apart electrodes, a DC voltage source operably connected across said electrodes for establishing an arc discharge current between said electrodes, an inductor connected in a series circuit with said voltage source and said electrodes for maintaining said arc discharge current at a substantially constant magnitude, a first switch means connected in circuit series with said voltage source, said inductor and said electrodes for opening and closing said series circuit, second switch means connected in circuit multiple with said inductor for shorting out said inductor prior to opening of said series circuit by said first switch means, and means connected in circuit parallel with said spaced-apart electrodes for delaying the establishment of an arc discharge between said electrodes until the voltage available across said electrodes is sufficient to maintain said arc discharge.
 4. The combination specified in claim 3 wherein said arc delaying means comprises, a fused horn gap means connected in circuit parallel with said electrodes and including a fusing wire selected to delay the establishment of an arc discharge between said electrodes until the voltage available across said electrodes is sufficient to maintain said arc discharge.
 5. The combination specified in claim 4 further including a starting wire means connected across said electrodes to facilitate the establishment of said arc discharge.
 6. The combination specified in claim 5 wherein said starting wire means is provided with a discontinuity adapted to relay the establishment of said arc discharge and further including, a monitoring resistor connected across the discontinuity in said starting wire to permit detection that the ends of said starting wire are in electrical contact with said electrodes. 